[2022/D09] Solved both tasks from today

1 files changed, 47 insertions, 0 deletions

diff --git a/2022/Day09/part-two.cl b/2022/Day09/part-two.cl
new file mode 100644
index 0000000..06f6623
--- /dev/null
+++ b/2022/Day09/part-two.cl
@@ -0,0 +1,47 @@
+;;; https://gitlab.com/Syndamia/senzill
+(require :senzill)
+(use-package :senzill.math)
+(use-package :senzill.collections)
+(use-package :senzill.pair)
+(use-package :senzill.io)
+
+(defparameter +rope-length+ 10)
+
+(ask-for-stream (prog-input)
+  (let ((rope '()) (visited '((0 . 0))))
+  (flet ((norm>sqrt2p (p) ; If c's eucledian length is less than sqrt(2). In other words, if c is outside the 3x3 square.
+           "Optimized version of (> (norm p) (sqrt 2))"
+           (or (> (abs (car p)) 1) (> (abs (cdr p)) 1)))
+
+         (dir-to-pair (direction)
+           (cond ((char= direction #\R) '( 1 .  0))
+                 ((char= direction #\L) '(-1 .  0))
+                 ((char= direction #\U) '( 0 .  1))
+                 ((char= direction #\D) '( 0 . -1)))))
+
+    (dotimes (i +rope-length+)
+      (push '(0 . 0) rope))
+
+    (doread-lines (inpt :read-line-options (prog-input NIL))
+                  (loop for i from 1 to (parse-integer inpt :start 2)
+                        for dirvec = (dir-to-pair (char inpt 0))
+
+                        do
+                        (pair+= (first rope) dirvec) ; First knot is the head
+                        ;;; We update the knot positions from left to right (from head to tail)
+                        ;;; Since each knot depends on the previous, we iterate from head to tail-1
+                        ;;; but always update "the second element" (from head+1 to tail)
+                        (loop for knot on rope
+                              while (cdr knot)
+                              for movec = (pair- (first knot) (second knot)) ; head - tail
+
+                              if (norm>sqrt2p movec)
+                                do
+                                ;; dist-resize so we don't put the knot on top of the other, but behind it
+                                (pair+= (second knot) (pair-round (dist-resize-by movec -1)))
+                              
+                              finally
+                                (if (not (member-if (lambda (x) (pair= x (car knot))) visited))
+                                  (push (car knot) visited)))))
+
+    (print (length visited)))))